KERALA AGRICULTURAL UNIVERSITY
AROMATIC AND MEDICINAL PLANTS RESEARCH STATION, ODAKKALI
EXTRACTION AND UTILISATION OF AROMATIC PLANTS
Essential, volatile or ethereal oils are mixtures composed of volatile liquid and solid compounds which vary widely in regard to their composition and boiling points. Plants owe their fragrance to presence of traces of essential oils in different parts. Numerous fragrance materials are present in roots, stems, barks, leaves, flowers, fruits and heartwoods.
Several processes like distillation, enfleurage, maceration, expression, solvent extraction and fluid extraction are available for extraction of aroma principles. Application of these processes, either singly or in combination depends upon nature of material and essential oil or absolute intended to be recovered.
Distillation may be defined as separation of components of a mixture of two or more liquids by virtue of difference in their vapour pressure.
The bulk of essential oils are produced by distillation. There are three systems of distillation‑ hydro, hydro‑steam and steam distillation.
Hydrodistillation though the oldest, is still being widely practised for oil extraction. The plant material is in direct contact with boiling water in a crude metallic distillation unit. The material floats on water or be completely immersed, depending upon its specific gravity and quantity of material handled per charge. Water is boiled by direct fire, steam jacket, closed steam coil or in a few cases open or perforated steam coil. Some plant materials like powdered almonds, rose petals and orange blossoms must be distilled while fully immersed and moving freely in boiling water, because on distillation with injected live steam (direct steam distillation) these materials agglutinate and form large compact lumps through which steam cannot penetrate.
b. Hydro‑steam distillation
Hydro‑steam distillation is employed where perfumery material is vulnerable to direct steam. Consequently, plant material is supported on a perforated grid or screen inserted at some distance above bottom of still. Lower part of still contains water up to a level just below grid. Water may be heated by any of the methods. Wet steam of low pressure rises through plant material. Typical features of this method are that steam is always fully saturated, wet and never superheated; besides plant material is in contact with steam only and not with boiling water.
c. Steam distillation
In steam distillation, live steam saturated or superheated, under pressure (up to 7 kg/cm2) is injected through steam tubes below the charge and pressure within the distillation vessel is controlled according to nature of the material being distilled. It resembles hydro-steam distillation except that no water is kept in bottom of still. This method is efficient and gives higher yields. However, it is not generally employed to delicate flowers.
Equipment for distillation
Equipment required for carrying on distillation of plant materials depends upon the size of operation and type of distillation to be used. There are, however three main parts which in varying size, form base for all three types of hydro distillation. The three universally employed parts are retort or still proper, condenser and oil separator. A fourth part namely, a separate steam boiler is necessary for steam distillation wherein direct live steam, often slightly superheated is required.
Retort: Retort or still proper commonly called as ‘tank’ serves primarily as a container for plant material and as a vessel in which water and or steam contacts plant material and vaporizes its essential oil.
Condenser: Condenser serves to convert all of steam and accompanying oil vapours into liquid.
Oil separator: Its function is to achieve a quick and complete separation of oil from condensed water. Since, total volume of water condensed will always be much greater than quantity of oil, it is necessary to remove the water continuously. Condensate flows from condenser into oil separator, where distillation water and volatile oil separate automatically.
II. Maceration (Extraction with hot fat)
In maceration, oil cells of fragrant flowers are ruptured by immersion in a hot fat or oil at 60‑70°C which in turn absorbs essential oils. Fat is separated from spent flowers and reused for absorbing fragrance from next batch of fresh flowers. Fat retained by flowers is recovered by hydraulic pressing. Resultant perfumed pomade is frequently marketed as such but is often extracted with strong alcohol to yield extracts. These alcoholic absolutes are absolutes of pomade in market parlance.
III. Enfleurage (Extraction with cold fat)
Enfleurage is the process of extraction of fragrance by absorbing it from flowers in contact with cold fats. This process is adopted for fragrant flowers of jasmine and tuberose, which continue to manifest their characteristic fragrance even in plucked condition. Solvents lack this virtue of arresting manifested fragrance.
Fats should be saturated and odourless to prevent entrance of fat odours. Refined lard or beef suet are preferred. Fat is thinly layered on both sides of a glass plate supported on a rectangular wooden frame or chassis. Fresh fragrant flowers are lightly layered on fat coated chassis. Several chassis are placed one above the other sandwiching the flowers between two layers of fat. Spent flowers are removed (defleurage) and fresh charge is made. Reversing of glass slab is called patage. Patage is done several times to obtain maximum perfume absorption. Furrows are created with combs to increase absorption surface. The process of defleurage, fresh charging and patage is continued to obtain fat of desired perfume strength.
Enfleurage gives a much greater yield of flower oil than other methods. Despite this advantage, enfleurage has lately been replaced by extraction with volatile solvents because enfleurage is a very delicate and lengthy process requiring much experience and labour.
IV. Extraction with volatile solvents
Principle of extraction with volatile solvents is simple. Fresh flowers are charged into specially constructed extractors and extracted systematically at room temperature, with a carefully purified solvent usually petroleum ether. Solvent penetrates flowers and dissolve natural flower perfume together with some waxes and albumins and colouring matter. Solution is subsequently pumped into an evaporator and concentrated at a low temperature. After the solvent is completely driven off in vacuum, concentrated flower oil is obtained. Thus, temperature applied during entire process is kept at a minimum; live steam as in case of distillation, does not exert its action upon delicate constituents of flower oil. Compared with distilled oils, extracted flower oils more truly represent natural perfume as originally present in flowers.
V. Super critical fluid extraction (SCFE) (Extraction using liquefied gases)
This is emerging as a versatile and important tool to separate components that are susceptible to thermal degradation. It is employed for extraction of flavours, fragrances and perfumes from a wide variety of natural products. This method of extraction is superior and faster than distillation. Higher diffusiveness and lower viscosities of supercritical fluids enable better penetration and faster equilibration. Besides, the solvent power is manipulable, free from surface tension and wetting properties and easily adoptable to isolate highly thermolabile compounds. Carbon dioxide is a favourite solvent by virtue of its cheapness, nontoxicity, noncorrosiveness, non‑flammability, easy to handle, needing mild processing conditions during extraction and good solvent power for alcohols, aldehydes, esters and ketones.
In this process, volatility and solubility are employed. Temperature and pressure variations are manipulated to utmost advantage. After extraction, solvent is separated from extract phase by varying operating conditions and is recycled after makeup.
Liquid carbon dioxide is completely miscible with components of essential oils like aldehydes, ketones, esters and alcohols. At same time, proteins, starches, mineral salts and water are insoluble in liquid carbon dioxide. Essential oils obtained by liquid carbon dioxide extraction are superior to that obtained through steam distillation and solvent extraction. Extraction of several natural products such as pyrethrins from chrysanthemum flower, essential oils from anise, caraway, clove, star anise, cinnamon and ginger are increasingly done by this process.
This method is employed when essential oils are thermosensitive. It is used for isolating essential oils from lemon and orange peels. In general, expression involves squeezing any plant material at great pressures to press out oils or other liquids. The process is carried out by hand-operated presses or crushes in isolated rural areas or by gigantic mechanical presses in industrial centres. In production of citrus juices, oil is unavoidably expressed from fruit. Oil is then separated from juice by centrifuging.
Some technical terms used in essential oil trade.
Attars are flower distillates collected over sandalwood oil. Accordingly, there are attars of jasmine, kewda, rose, champaca, khus, maulsari (Mimussops elengi L.) kadamba (Anthocephalus cadamba Miq.) and mango. Attars are prepared by washing sandalwood oil with one middle and tail distillate from a previous batch to remove lower terpenes from the oil sweetening attar into a mellow and fragrant note. Vapours from water‑distillation still are condensed and absorbed in aforesaid washed sandalwood oil. Base oil is then charged to forerunnings of a fresh batch of perfumery plant materials, while tail runnings are employed for preparation of a new batch of base oil. Distillation with fresh charges is repeated till required concentration of natural oil in base oil is obtained. Attars being more stable have longer shelf life. Quantum of flower oil in the product determines quality and price of attar. Attars are used for perfuming tobacco, soaps, agarbathis and hair oils. Alcoholic solutions of attars are now available.
ii. Floral and aromatic waters
These are prepared by distilling fragrant materials with water. A specific quantity of fragrant materials is distilled with a specified volume of water for a specific period and a predetermined volume of distillate is collected as per individual formulae of manufacturers. These waters are prepared and marketed as single, double or triple distilled water. These are employed for perfume wafting at sacred places and during social functions. It is also added in traces to cold clean drinking waters.
Agarbathis are the Indian version of Chinese joss sticks and dhoop is of incense. Both are burnt slowly to obtain a fragrant smoke. These too have their religious, aesthetic and secular uses. Some industrial houses procure raw agarbathis, add perfumes, pack and market them.
iv. Perfumery grade alcohol
This is required as diluent and solvent for production of high class perfumes and flavours, for which olfactory quality of alcohol is a basic and essential requirement. It must be free from higher alcohols and aldehydes. Such alcohols are technically denoted as Extra Neutral Alcohol and commercially called silent spirit, manufactured from rectified spirit of 90 to 95 % purity obtained from molasses or grains by double or triple fractionation.
v. Flavour encapsulation systems
Flavour encapsulation systems like spray drying, spray cooling, spray chilling, gelatin encapsulation, and cold encapsulation are now increasingly being used by the industry. Spray drying converts a liquid into powder in one step process. Liquid to be dried (feed) is atomized in a stainless steel drying chamber by a nozzle or a rotating disc into a spray which instantly comes into contact with drying air. Due to rapid evaporation, temperature of droplets can be kept far below drying air temperature and is normally 15‑20ºC below outlet air temperature. Flavour to be encapsulated is specifically formulated to have the highest strength and added to encapsulating medium like gum acacia and modern carriers from modified starches. Carrier choice depends upon emulsification properties, low viscosity in solution at high solid content, flavour retention ability, hygroscopicity, blend flavour compatibility in finished products and stability during storage
Absolute is a prepared perfume material. It is a concentrate, entirely alcohol soluble and usually liquid perfume materials. They are obtained by alcohol extraction of concretes or other hydrocarbon types of extracts or from fat extract of plant materials.
It is a non-purified form of essential oil obtained mostly by means of solvent extraction where essential oil, plant pigments and waxes are present. From concrete, absolute is obtained. Concrete may yield about 45-55% of absolute on a weight basis.
An extract is an alcoholic solution of odorous part of a pomade. This is an intermediate product in preparation of absolutes from pomades.
In perfumery, a fixative means a material which slows down rate of evaporation of more volatile material in a perfume composition; eg. Sandalwood, patchouli.
An oleoresin is either a natural or prepared material. Natural oleoresins are exudation from tree- trunks and bark. (elm, turpentine, copaiba, balsam). The prepared oleoresins, on other hand are liquid preparations, extracted from plants with help of solvents which can extract oil and resinous matter (pepper, ginger). They consist entirely or mainly of essential oil and resins.
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